How to put data into GUI

I'm making a GUI, and I have figured out how to put in push buttons and insert functions that supposedly connect to them, but when I run the GUI it is blank except for the push buttons. I am wondering how to insert data that is not set in the GUI so it can be changed by whoever is viewing it and applied to different data. Is this possible, or does the GUI have to be rewritten every time the data changes? What is the best way to put a set of data into a GUI? (I have MATLAB_R2015a.)